Refrigerating machine oil composition

ABSTRACT

A refrigerating machine oil composition according to the invention comprises an alicyclic polycarboxylic acid ester compound obtained from the following compounds (a) to (c):  
     (a) an alicyclic polycarboxylic acid having an alicyclic ring and two or more carboxyl groups, or its derivative, wherein at least two of the carboxyl groups are bonded to mutually adjacent carbon atoms on the alicyclic ring;  
     (b) a compound with two or more hydroxyl groups or its derivative; and  
     (c) a compound with one hydroxyl group or its derivative.  
     It can be used together with HFC refrigerants and natural refrigerants such as carbon dioxide and hydrocarbons, to provide a satisfactory balance between all of the properties of lubricity, miscibility with refrigerants, heat and hydrolytic stability and electric insulating property.

TECHNICAL FIELD

[0001] The present invention relates to a refrigerating machine oilcomposition, and specifically it relates to a refrigerating machine oilcomposition comprising an alicyclic polycarboxylic acid ester compound.

BACKGROUND ART

[0002] In recent years, the issues of refrigerant substitution andrefrigerating system efficiency improvement have been studied from thestandpoint of minimizing ozone layer destruction and global warning. Inthe area of refrigerant substitutes, progress is being made in thesubstitution of HFCs (hydrofluorocarbons) for chlorine-containingrefrigerants such as CFCs (chlorofluorocarbons) and HCFCs(hydrochlorofluorocarbons) On the other hand, since HFC refrigerantscould be subject to restrictions in light of the problem of globalwarming, natural refrigerants such as carbon dioxide, ammonia andhydrocarbons are also being researched for applied use.

[0003] Efforts toward such refrigerant substitution are advancing inparallel with development of refrigerating machine oils for thesesubstitute refrigerants. Refrigerating machine oils must satisfy anumber of performance requirements including lubricity, miscibility withrefrigerants, heat and hydrolytic stability, electric insulatingproperty and low hygroscopicity, and therefore compounds satisfyingthese requirements are selected to match the type and purpose of use ofeach refrigerant. Examples of refrigerating machine oils used for HFCsinclude oxygen-containing compounds such as esters, ethers andcarbonates that are miscible with the refrigerants, and alkylbenzeneswhich have inferior miscibility with the refrigerants but have excellentlubricity and heat and hydrolytic stability.

[0004] At the same time, efforts are being made to lower the viscosityof refrigerating machine oils with the goal of achieving higherefficiency of refrigerating systems. Known ester-based refrigerator oilsinclude polyol esters obtained by reaction of aliphatic polyhydricalcohols and fatty acids, as disclosed in Japanese TranslationPublication No. HEI 3-505602 (JP-A 3-505602) of InternationalPublication for Patent Application and Japanese Patent Kokai (Laid-Open)Publication No. HEI 3-128991 (JP-A 3-128991), and for reduction of theviscosity of such ester-based refrigerating machine oils it has beenfound effective to select fatty acids with low carbon number alkylgroups for use in the raw material. However, fatty acids with loweralkyl groups generally produce the undesirable situation of low heat andhydrolytic stability of the obtained esters. On the other hand, fattyacids with high carbon number alkyl groups are selected in order toincrease the viscosity of such esters, but this creates a problem inthat sufficient miscibility with refrigerants cannot be achieved.

[0005] There are also known alicyclic polycarboxylic acid esters, suchas disclosed in Japanese Patent Kokai (Laid-Open) Publication No. HEI9-221690 (JP-A 9-221690), as ester-based refrigerating machine oils withexcellent heat and hydrolytic stability, but those with a large numberof carbon atoms in the terminal alkyl group at the ester site haveinsufficient miscibility with refrigerants, while those with a smallnumber of carbon atoms in the terminal alkyl group have inferior heatand hydrolytic stability, as well as insufficient lubricity.

[0006] There has yet to be developed, therefore, an ester-basedrefrigerating machine oil that has a satisfactory balance of lubricity,heat and hydrolytic stability and refrigerant miscibility, while alsosatisfying the other required aspects of performance such as electricinsulating property.

DISCLOSURE OF THE INVENTION

[0007] It is an object of the present invention, which has beenaccomplished in light of the aforementioned problems of the prior art,to provide a refrigerating machine oil composition which has asatisfactory balance of lubricity, refrigerant miscibility, heat andhydrolytic stability and electrical insulating property when usedtogether with HFC refrigerants or natural refrigerants such as carbondioxide and hydrocarbons.

[0008] As a result of diligent research aimed at achieving this object,the present inventors have completed the present invention upon findingthat the aforementioned problems are solved by using an alicyclicpolycarboxylic acid ester compound obtained from a specific acidcomponent and a specific alcohol component.

[0009] Namely, the refrigerating machine oil composition of theinvention comprises an alicyclic polycarboxylic acid ester compoundobtained from the following compounds (a) to (c);

[0010] (a) an alicyclic polycarboxylic acid having an alicyclic ring andtwo or more carboxyl groups, or its derivative, wherein at least two ofthe carboxyl groups are bonded to mutually adjacent carbon atoms on thealicyclic ring;

[0011] (b) a compound with two or more hydroxyl groups or itsderivative; and

[0012] (c) a compound with one hydroxyl group or its derivatives

[0013] According to the invention, the number of carboxyl groups ofcoinpound (a) is preferably 2, and the number of hydroxyl groups ofcompound (b) is preferably 2.

[0014] Moreover, according to the invention, compound (c) is preferablya mixture of

[0015] at least one type of monohydric alcohol selected from the groupconsisting of aliphatic monohydric alcohols of 1-5 carbons and

[0016] at least one type of monohydric alcohol selected from the groupconsisting of aliphatic monohydric alcohols of 6-18 carbons.

[0017] In addition, the refrigerating machine oil composition of theinvention preferably also comprises at least one selected from the groupconsisting of is phosphoric acid esters, acidic phosphoric acid esters,amine salts of acidic phosphoric acid ester, chlorinated phosphoric acidesters and phosphorous acid esters.

[0018] The refrigerating machine oil composition of the inventionpreferably further comprises at least one selected from the groupconsisting of phenylglycidyl ether-type epoxy compounds, alkylglycidylether-type epoxy compounds, glycidyl ester-type epoxy compounds,allyloxirane compounds, alkyloxirane compounds, alicyclic epoxycompounds, epoxidized fatty acid monoesters and epoxidized vegetableoils.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] A preferred mode for the present invention will now be explainedin detail.

[0020] The refrigerating machine oil composition of the inventioncomprises an alicyclic polycarboxylic acid ester compound obtained fromthe following compounds (a) to (c);

[0021] (a) an alicyclic polycarboxylic acid having an alicyclic ring andtwo or more carboxyl groups, or its derivative, wherein at least two ofthe carboxyl groups are bonded to mutually adjacent carbon atoms on thealicyclic ring;

[0022] (b) a compound with two or more hydroxyl groups or itsderivative; and

[0023] (c) a compound with one hydroxyl group or its derivative.

[0024] The (a) alicyclic polycarboxylic acid or its derivative used asthe acid component for the invention must comprise an alicyclic ring andat least 2 carboxyl groups (such compounds will hereunder becollectively referred to as compound (a), including alicyclicpolycarboxylic acid derivatives). If only one carboxyl group is present,the refrigerant miscibility and heat and hydrolytic stability areinsufficient. While there is no particular limit to the number ofcarboxyl groups, it is preferably no greater than 4, more preferably nogreater than 3 and most preferably no greater than 2. If the number ofcarboxyl groups exceeds this range, the low temperature flow propertiesof the obtained alicyclic polycarboxylic acid ester compound tend to beinadequate.

[0025] Furthermore, at least 2 of the carboxyl groups of compound (a)according to the invention must be bonded to mutually adjacent carbonatoms on the alicyclic ring. Without 2 carboxyl groups bonded tomutually adjacent carbon atoms on the alicyclic ring, the obtainedalicyclic polycarboxylic acid ester has insufficient heat and hydrolyticstability.

[0026] When compound (a) used for the invention is an alicyclicpolycarboxylic acid there are no particular restrictions on the stericconfiguration of the carboxyl groups, and the orientation of thecarboxyl groups bonded to the mutually adjacent carbon atoms on thealicyclic ring may be the cis-form or trans-form. Also, cis-forms aloneor trans-forms alone may be used, or mixtures of both may be used.However, cis-forms are preferred from the standpoint of heat andhydrolytic stability, while trans-forms are preferred from thestandpoint of both heat and hydrolytic stability and lubricity. When amixture of cis-forms and trans-forms is used, the molar ratio ispreferably from 20/80 to 80/20, more preferably from 25/75 to 75/25 andeven more preferably from 30/70 to 70/30. If the molar ratio ofcis-forms and trans-forms is within these ranges, it is possible toachieve both higher lubricity and superior heat and hydrolyticstability.

[0027] As alicyclic polycarboxylic acids according to the inventionthere may be mentioned cycloalkanepolycarboxylic acids,cycloalkenepolycarboxylic acids and the like having at least twocarboxyl groups bonded to mutually adjacent carbon atoms on thealicyclic ring, and any of these may be used alone or in combinations oftwo or more types. Specific examples of alicyclic polycarboxylic acidswith such a structure include 1,2-cyclohexanedicarboxylic acid,4-cyclohexene-1,2-dicarboxylic acid, 1-cyclohexene-1,2-dicarboxylicacid, 3-methyl-1,2-cyclohexanedicarboxylic acid,4-methyl-1,2-cyclobexanedicarboxylic acid,3-methyl-4-cyclohexene-1,2-dicarboxylic acid,4-methyl-4-cyclohexene-1,2-dicarboxylic acid,1,2,4-cyclohexanetricarboxylic acid and1,2,4,5-cyclohexanetetracarboxylic acid. Of these,1,2-cyclohexanedicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylicacid, 4-methyl-1,2-cyclohexanedicarboxylic acid,1,2,4-cyclohexanetricarboxylic acid and1,2,4,5-cyclohexanetetracarboxylic acid are preferred from thestandpoint of low rise ill viscosity during use of the obtainedalicyclic polycarboxylic acid ester compound under prolonged and severeconditions, while 4-cyclohexene-1,2-dicarboxylic acid,1-cyclohexene-1,2-dicarboxylic acid,4-methyl-1,2-cyclohexanedicarboxylic acid,3-methyl-4-cyclohexene-1,2-dicarboxylic acid and4-methyl-4-cyclohexene-1,2-dicarboxylic acid are preferred from thestandpoint of low rise in total acid value during use under prolongedand severe conditions.

[0028] Also, compound (a) according to the invention may be an alicyclicpolycarboxylic acid derivative such as an acid anhydride, ester or acidhalide. As alicyclic polycarboxylic acid derivatives to be used for theinvention there may be mentioned acid anhydrides, esters and acidhalides of the compounds mentioned above in explanation of the alicyclicpolycarboxylic acid.

[0029] There are no particular restrictions on the process for producingthe alicyclic, polycarboxylic acid or its derivative, and any desiredprocess may be employed. As a specific example,4-cyclohexene-1,2-dicarboxylic acid may be obtained by reactingbutadiene and maleic anhydride in a benzene solvent at 100° C.

[0030] Compound (b) which is one of the alcohol components used for theinvention must have at least two hydroxyl groups. As such examples forcompound (b) there may be mentioned polyhydric alcohols, polyhydricphenols, polyhydric aminoalcohols and their condensates, as well ascompounds obtained by esterification of the hydroxyl groups of thesecompounds with lower carboxylic acids such as acetic acid (these willhereunder be collectively referred to as compound (b), includingderivatives of compounds with 2 or more hydroxyl groups). Among these,the use of polyhydric alcohols or their condensates tends to improve therefrigerant miscibility, electrical insulating property and heatstability.

[0031] Polyhydric alcohols that may be suitably used for the inventionpreferably have 2-10 carbons and more preferably 2-8 carbons, and mayinclude an ether bond in the molecule. As specific examples of suchpolyhydric alcohols there may be mentioned ethylene glycol, propyleneglycol, butylene glycol, 1,3-butanediol, 1,4-butanediol, glycerin,neopentylglycol, trimethylolethane, trimethylolpropane,trimethylolbutane, pentaerythritol, 1,3,5-pentanetriol, sorbitol,sorbitan, isosorbide, sorbitolglycerin condensate, adonitol, arabitol,xylitol, mannitol, xylose, arabinose, ribose, rhamnose, glucose,fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose,trehalose, sucrose, raffinose, gentianose, melezitose, methylglucosideand their partial etherified products.

[0032] Polyhydric alcohol condensates that may be suitably used for theinvention are obtained by condensation of polyhydric alcohols withpreferably 2-10 carbons and more preferably 2-8 carbons. From thestandpoint of electrical properties and ease of production, the degreeof condensation of such polyhydric alcohol condensates is preferably2-10, and more preferably 2-5. As specific examples of polyhydricalcohol condensates with such a structure there may be mentioneddiethylene glycol, triethylene glycol, tetraethylene glycol,pentaethylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, pentapropylene glycol, dibutylene glycol,tributylene glycol, tetrabutylene glycol, pentabutylene glycol,diglycerin, triglycerin, tetraglycerin, pentaglycerin,di(neopentylglycol), tri(neopentylglycol), tetra(neopentylglycol),penta(neopentylglycol), di(trimethylolethane), tri(trimethylolethane),tetra(trimethylolethane), penta(trimethylolethane),di(trimethylolpropane), tri(trimethylolpropane),tetra(trimethylolpropane), penta(trimethylolpropane),di(trimethylolbutane), tri(trimethylolbutane), tetra(trimethylolbutane),penta(trimethylolbutane), di(pentaerythritol), tri(pentaerythritol),tetra(pentaerythritol) and penta(pentaerythritol).

[0033] Compound (b) which is used as one of the alcohol components forthe invention may be a derivative having the hydroxyl groups esterifiedby a lower carboxylic acid, as mentioned above. As such derivativesthere may be suitably used acetic acid esters and propionic acid estersof the compounds mentioned above as polyhydric alcohols and polyhydricalcohol condensates.

[0034] Compound (c) which is used as the other alcohol component for theinvention must have one hydroxyl group. As examples of the compound (c)there may be mentioned monohydric alcohols, monohydric phenols,monohydric aminoalcohols and these compounds having the hydroxyl groupsesterified with lower carboxylic acids such as acetic acid (suchderivatives will also be included hereunder as compound (c)). Preferredfor use among these are straight chain monohydric alcohols of 3-18carbons, branched chain monohydric alcohols of 3-18 carbons andmonohydric cycloalcohols of 5-10 carbons. As such monohydric alcoholsthere may be mentioned, specifically, straight or branched chainpropanols (including n-propanol, 1-methylethanol, etc.), straight orbranched chain butanols (including n-butanol, 1-methylpropanol,2-methylpropanol, etc.), straight or branched chain pentanols (includingn-pentanol, 1-methylbutanol, 2-methylbutanol, 3-methylbutanol, etc.),straight or branched chain hexanols (including n-hexanol,1-methylpentanoyl, 2-methylpentanol, 3-methylpentanol, etc.), straightor branched chain heptanols (including n-heptanol, 1-methylhexanol,2-methylhexanol, 3-methylhexanol, 4-methylhexanol, 5-methylhexanol,2,4-dimethylpentanol, etc.), straight or branched chain octanols(including n-octanol, 2-ethylhexanol, 1-methylpentanol,2-methylheptanol, etc.), straight or branched chain nonanols (includingn-nonanol, 1-methyloctanol, 3,5,5-trimethylhexanol,1-(2′-methylpropyl)-3-methylbutanol, etc.), straight or branched chaindecanols (including n-decanol, iso-decanol, etc.), straight or branchedchain undecanols (including n-undecanol, etc.), straight or branchedchain dodecanols (including n-dodecanol, iso-dodecanol, etc.), straightor branched chain tridecanols, straight or branched chain tetradecanols(including n-tetradecanol, iso-tetradecanol, etc.), straight or branchedchain pentadecanols, straight or branched chain hexadecanols (includingn-hexadecanol, iso-hexadecanol, etc.), straight or branched chainheptadecanols, straight or branched chain octadecanols (includingn-octadecanol, iso-octadecanol, etc.), cyclohexanol, methylcyclohexanol,dimethylcyclohexanol, and the like.

[0035] It is particularly preferred to use as compound (c) a mixture of

[0036] (c-I) at least one type of monohydric alcohol selected from thegroup consisting of aliphatic monohydric alcohols of 1-5 carbons, and

[0037] (c-II) at least one type of monohydric alcohol selected from thegroup consisting of aliphatic monohydric alcohols of 6-18 carbons,

[0038] in order to obtain sufficiently high heat and hydrolyticstability and lubricity, as well as superior miscibility withrefrigerants. When only one type of alcohol or the aforementioned group(c-I) is used, the obtained alicyclic dicarboxylic acid ester compoundexhibits inferior heat and hydrolytic stability, while also tending tohave insufficient lubricity. When only one type of alcohol of theaforementioned group (c-II) is used, the obtained alicyclic dicarboxylicacid ester compound tends to have insufficient miscibility withrefrigerants.

[0039] Moreover, the alicyclic dicarboxylic acid ester compound of theinvention is preferably obtained using two or more different alcohols ascompound (c), and it is particularly preferred to use both an alcoholcomponent of (c-I) and an alcohol component of (c-II). Even when two ormore different types only among alcohol components of (c-I) are used ascompound (c), the obtained alicyclic dicarboxylic acid ester compoundtends to have inferior heat and hydrolytic stability, as well asinsufficient lubricity Furthermore, even when two or more differenttypes only from among alcohol components of (c-II) are used, theobtained alicyclic dicarboxylic acid ester compound tends to haveinsufficient miscibility with refrigerants.

[0040] As alcohol components of (c-I) there may be mentioned straightchain alcohols of 1-5 carbons and branched chain alcohols of 3-5carbons, specific examples of which include methanol, ethanol,n-propanol, n-butanol, n-pentanol, iso-propanol, iso-butanol,sec-butanol and iso-pentanol. From the standpoint of lubricity,n-butanol and n-pentanol are preferred among these, while iso-butanoland iso-pentanol are preferred from the standpoint of heat andhydrolytic stability.

[0041] As alcohol components of (c-II) there may be mentioned straightchain alcohols of 6-18 carbons and branched chain alcohols of 6-18carbons, specific examples of which include n-hexanol, n-heptanol,n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol,n-tetradecanol, n-hexadecanol, n-octadecanol, iso-hexanol,2-methylhexanol, 1-methylheptanol, 2-methylheptanol, iso-heptanol,2-ethylhexanol, 2-octanol, iso-octanol, 3,5,5-trimethylhexanol,iso-decanol, iso-tetradecanol, iso-hexadecanol, iso-octadecanol and2,6-dimethyl-4-heptanol. From the standpoint of both lubricity andmiscibility, n-heptanol, n-octanol, n-nonanol and n-decanol arepreferred among these, while iso-heptanol, 2-ethylhexanol and3,5,5-trimethylhexanol are preferred from the standpoint of bothmiscibility and heat and hydrolytic stability.

[0042] When a (c-I) component and a (c-II) component are used togetherthere are no particular restrictions on the molar ratio of the (c-I)component and the (c-II) component, but it is preferably in the range of1:99 to 99:1 in order to simultaneously satisfy the required lubricity,heat and hydrolytic stability and refrigerant miscibility. From astandpoint focused on the miscibility, this ratio is preferably in therange of 60:40 to 99:1, more preferably in the range of 70:30 to 99:1and most preferably in the range of 80;20 to 99:1. From a standpointfocused on the heat and hydrolytic stability and lubricity, the ratio ispreferably in the range of 1:99 to 60:40, more preferably in the rangeof 1:99 to 50:50 and most preferably in the range of 1:99 to 40:60.

[0043] Compound (c) used as an alcohol component according to theinvention may be a derivative wherein the hydroxyl group is esterifiedwith a lower carboxylic acid. As such derivatives there may be suitablyused acetic acid esters and propionic acid esters of the compoundsmentioned above in explanation of the monohydric alcohol.

[0044] According to the invention, the following combination ofcompounds (a′),(b′) and (c′) are preferred as compounds (a), (b) and(c).

[0045] (a′) At least one selected froth the group consisting of1,2-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acidand their acid anhydrides, esters and acid halides;

[0046] (b′) At least one selected from the group consisting of ethyleneglycol, propylene glycol, butylene glycol, glycerin, neopentyl glycol,diethylene glycol, dipropylene glycol, dibutylene glycol, diglycerin,dineopentyl glycol and their esters; and

[0047] (c′) at least one selected from the group consisting ofn-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol,n-decanol, iso-butanol, iso-pentanol, iso-hexanol, iso-heptanol,2-ethylhexanol, 3,5,5-trimethylhexanol, mixed alcohols of n-butanol andn-hexanol, mixed alcohols of n-butanol and n-heptanol, mixed alcohols ofn-butanol and n-octanol, mixed alcohols of n-butanol and n-nonanol,mixed alcohols of n-butanol and n-decanol, mixed alcohols of n-butanoland iso-hexanol, mixed alcohols of n-butanol and iso-heptanol, mixedalcohols of n-butanol and 2-ethylhexanol, mixed alcohols of n-butanoland 3,5,5-trimethylhexanol, mixed alcohols of iso-butanol and n-hexanol,mixed alcohols of iso-butanol and n-heptanol, mixed alcohols ofiso-butanol and n-octanol, mixed alcohols of iso-butanol and n-nonanol,mixed alcohols of iso-butanol and n-decanol, mixed alcohols ofiso-butanol and iso-hexanol, mixed alcohols of iso-butanol andiso-heptanol, mixed alcohols of iso-butanol and 2-ethylhexanol, mixedalcohols of iso-butanol and 3,5,5-trimethylhexanol, mixed alcohols ofn-pentanol and n-hexanol, mixed alcohols of n-pentanol and n-heptanol,mixed alcohols of n-pentanol and n-octanol, mixed alcohols of n-pentanoland n-nonanol, mixed alcohols of n-pentanol and n-decanol, mixedalcohols of n-pentanol and iso-hexanol, mixed alcohols of n-pentanol andiso-heptanol, mixed alcohols of n-pentanol and 2-ethylhexanol, mixedalcohols of n-pentanol and 3,5,5-trimethylhexanol, mixed alcohols ofiso-pentanol and n-hexanol, mixed alcohols of iso-pentanol andn-heptanol, mixed alcohols of iso-pentanol and n-octanol, mixed alcoholsof iso-pentanol and n-nonanol, mixed alcohols of iso-pentanol andn-decanol, mixed alcohols of iso-pentanol and iso-hexanol, mixedalcohols of iso-pentanol and iso-heptanol, mixed alcohols ofiso-pentanol and 2-ethylhexanol, mixed alcohols of iso-pentanol,3,5,5-trimethylhexanol, and their esters.

[0048] The total amount of the alcohols of compound (b) and compound (c)for esterification reaction using the aforementioned compounds (a) to(c) is usually 1.0-1.5 equivalents and preferably 1.05-1.2 equivalentsto one equivalent of the (a) alicyclic polycarboxylic acid or itsanhydride.

[0049] The molar ratio of compound (b) and compound (c) is notparticularly limited, but a range of 1:99 to 99:1 is preferred becauseit can simultaneously provide satisfactory lubricity, heat andhydrolytic stability and miscibility with refrigerants. From astandpoint focused on miscibility, the ratio is preferably in the rangeof 1:99 to 80:20, more preferably in the range of 5:95 to 70:30 and mostpreferably in the range of 10:90 to 60:40.

[0050] The alicyclic polycarboxylic acid ester compound of the inventionis prepared by esterification of the acid component (a) and alcoholcomponents (b) and (c) according to a common process, preferably in aninert gas atmosphere of nitrogen or the like, with heating either in thepresence of or in the absence of an esterification catalyst.

[0051] When a lower alcohol ester of an alicyclic dicarboxylic acid isused as compound (a), or when an acetic acid ester or propionic acidester of an alcohol is used as compound (b) or (c), it is possible toobtain an alicyclic dicarboxylic acid ester compound according to theinvention by ester exchange reaction.

[0052] Examples of esterification catalysts for the esterificationreaction include Lewis acids such as aluminum derivatives, tinderivatives and titanium derivatives; alkali metal salts such as sodiumalkoxides and potassium alkoxides; and sulfonic acids such aspara-toluenesulfonic acid, methanesulfonic acid and sulfuric acid, amongwhich Lewis acids such as aluminum derivatives, tin derivatives andtitanium derivatives are preferred in consideration of the effect on theheat and hydrolytic stability of the obtained alicyclic dicarboxylicacid ester compound, with tin derivatives being particularly preferredfrom the standpoint of reaction efficiency. The amount of esterifyingcatalyst used may be, for example, about 0.1-1% by mass with respect tothe total of the acid component and alcohol component raw materials.

[0053] The reaction temperature for the esterification is typically150-230° C., and the reaction is usually complete by 3 to 30 hours.

[0054] After completion of the esterification reaction, the excess rawmaterials are distilled off under reduced pressure or under ordinarypressure, and then a common purification method such as liquid/liquidextraction, reduced pressure distillation, or adsorption purificationtreatment such as active carbon treatment, may be employed to purify theester compound.

[0055] When, for the esterification reaction, the polycarboxylic acid orits derivative used as compound (a) has two carboxyl groups and thecompound used as compound (b) has two hydroxyl groups, the reactionproduct will generally encompass compounds represented by the followingformulas (A) to (E):

R²—X—R¹—X—R²  (A)

R²—X—R¹—X—R¹—X—R²  (B)

[0056]

 R²—X—R²  (E)

[0057] where X represents an alicyclic dicarboxylic acid residue derivedfrom compound (a), R¹ represents the residue of a compound with 2hydroxyl groups derived from compound (b), and R² represents the residueof a compound with one hydroxyl group derived from compound (c).

[0058] The alicyclic dicarboxylic acid residues represented by X informulas (A) to (E) above are groups wherein carboxyl groups are bondedto mutually adjacent carbon atoms on an alicyclic ring such as acyclopentane ring, cyclopentene ring, cyclohexane ring, cyclohexenering, cycloheptane ring or cycloheptene ring. Preferred for suchalicyclic dicarboxylic acid residues are groups with cyclohexane ringsand cyclohexene rings. Groups with cyclohexane rings are more preferredamong these because of their low rise in viscosity during use underprolonged and severe conditions, while cyclohexene rings are even morepreferred because of their low rise in total acid value during use underprolonged and severe conditions.

[0059] The groups represented by R¹ in formulas (A) to (E) above areresidues of compounds with 2 hydroxyl groups used as compound (b), fromwhich the hydroxyl groups have been removed.

[0060] When a dihydric alcohol is used as compound (b), R¹ may includean ether bond, and it preferably has 2-10 carbons and more preferably2-8 carbons. As specific examples of R¹ there may be mentioned residuesof compounds such as ethylene glycol, propylene glycol, butylene glycol,1,3-butanediol, 1,4-butanediol and neopentylglycol with the hydroxylgroups removed.

[0061] When a condensate of a dihydric alcohol is used as compound (b),R¹ is preferably a residue of a condensate with 2-10 (preferably 2-8)carbons and a condensation degree of 2-10 (preferably 2-5). As specificexamples of R¹ there may be mentioned residues of compounds such asdiethylene glycol, triethylene glycol, tetraethylene glycol,pentaethylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, pentapropylene glycol, dibutylene glycol,tributylene glycol, tetrabutylene glycol, pentabutylene glycol,di(neopentylglycol), tri(neopentylglycol), tetra(neopentylglycol) andpenta(neopentylglycol), with the hydroxyl groups removed.

[0062] The groups represented by R² in formulas (A) to (E) above areresidues of compounds with one hydroxyl group used as compound (c), withthe hydroxyl group removed. R² preferably has 1-30 carbons, morepreferably 2-24 carbons and even more preferably 3-18 carbons. As groupsfor R² there may be mentioned alkyl groups, alkenyl groups, cycloalkylgroups, alkylcycloalkyl groups, aryl groups, alkylaryl groups andarylalkyl groups. Alkyl groups, cycloalkyl groups and alkylcycloalkylgroups are preferred among these from the standpoint of heat andhydrolytic stability.

[0063] Of the groups represented by R², the alkyl groups may be eitherstraight or branched chain. As specific examples of alkyl groups of 3-18carbons there may be mentioned straight or branched chain propyl group,straight or branched chain butyl group, straight or branched chainpentyl group, straight or branched chain hexyl group, straight orbranched chain heptyl group, straight or branched chain octyl group,straight or branched chain nonyl group, straight or branched chain decylgroup, straight or branched chain undecyl group, straight or branchedchain octyl group, straight or branched chain tridecyl group, straightor branched chain tetradecyl group, straight or branched chainpentadecyl group, straight or branched chain hexadecyl group, straightor branched chain heptadecyl group and straight or branched chainoctadecyl group.

[0064] Of these alkyl groups, straight chain alkyl groups of 4 or morecarbons are preferred from the standpoint of heat and hydrolyticstability, while those of no greater than 18 carbons are preferred fromthe standpoint of refrigerant miscibility. Branched chain alkyl groupsof 3 or more carbons are preferred from the standpoint of heat andhydrolytic stability, while those of no greater than 18 carbons arepreferred from the standpoint of refrigerant miscibility.

[0065] As cycloalkyl groups represented by R² there may be mentionedcyclopentyl group, cyclohexyl group and cycloheptyl group, withcyclohexyl group being preferred from the standpoint of heat andhydrolytic stability. An alkylcycloalkyl group is one having an alkylgroup bonded to a cycloalkyl group, and those with alkyl groups bondedto cyclohexyl are preferred from the standpoint of heat and hydrolyticstability. Preferred alkylcycloalkyl groups are also those with a totalof 6 or more carbons from the standpoint of heat and hydrolyticstability, and those with no more than a total of 10 carbons from thestandpoint of refrigerant miscibility and low temperature flowproperties.

[0066] When a mixed alcohol of monohydric alcohols of (c-I) and (c-II)is used as compound (c), the alkyl group derived from component (c-I) ofthe R² groups of the obtained compounds (A) to (E) is an alkyl group of1-5 carbons, and preferably an alkyl group of 3-5 carbons from thestandpoint of beat and hydrolytic stability.

[0067] The alkyl group of 1-5 carbons derived from component (c-I) maybe straight or branched chain, but straight chain alkyl groups arepreferred from the standpoint of lubricity, while branched chain alkylgroups are preferred from the standpoint of refrigerant miscibility andheat and hydrolytic stability. As specific examples of such alkyl groupsthere may be mentioned methyl group, ethyl group, straight or branchedchain propyl group, straight or branched chain butyl group, straight orbranched chain pentyl group and the like, among which n-butyl group andn-pentyl group are preferred from the standpoint of lubricity, whileiso-butyl group and iso-pentyl group are preferred from the standpointof heat and hydrolytic stability.

[0068] The alkyl group derived from component (c-II) of the R² groups ofthe aforementioned compounds (A) to (E) is an alkyl group of 6-18carbons, and from the standpoint of miscibility, it is preferably analkyl group of 6-12 carbons and even more preferably an alkyl group of7-9 carbons. An alkyl group of 6-18 carbons may be straight or branchedchain, but straight chain alkyl groups are preferred from the standpointof lubricity, while branched chain alkyl groups are preferred from thestandpoint of miscibility and heat and hydrolytic stability. The alkylgroup preferably has no more than 18 carbons as this results in inferiorrefrigerant miscibility and low temperature flow properties.

[0069] As specific examples of alkyl groups of 6-18 carbons derived fromcomponent (c-II) there may be mentioned straight or branched chain hexylgroup, straight or branched chain heptyl group, straight or branchedchain octyl group, straight or branched chain nonyl group, straight orbranched chain decyl group, straight or branched chain undecyl group,straight or branched chain dodecyl group, straight or branched chaintridecyl group, straight or branched chain tetradecyl group, straight orbranched chain pentadecyl group, straight or branched chain hexadecylgroup, straight or branched chain heptadecyl group and straight orbranched chain octadecyl group, among which n-heptyl group, n-octylgroup, n-nonyl group arid n-decyl group are preferred from thestandpoint of both lubricity and miscibility, while iso-heptyl group,2-ethylhexyl group and 3,5,5-trimethylhexyl group are preferred from thestandpoint of both miscibility and heat and hydrolytic stability.

[0070] When an alcohol of component (c-I) and an alcohol of component(c-II) are used for compound (c), the compounds represented by formulas(A), (B) and (E) above will include the following (I) to (III):

[0071] (I) Esters wherein one of the two alkyl groups represented by R²in the same molecule is a group derived from component (c-I) and theother is a group derived from component (c-II);

[0072] (II) Mixtures of esters wherein both ester groups represented byR² in the same molecule are groups derived from component (c-I) andesters wherein the two ester groups represented by R² in the samemolecule are groups derived from component (c-II); and

[0073] (III) Mixtures of (I) and (II).

[0074] According to the invention, any of the modes of (I) to (III) maybe used, although (I) or (III) is preferred from the standpoint of heatand hydrolytic stability.

[0075] For (III), there is no particular limit on the proportion of (I)and (II), but from the standpoint of heat and hydrolytic stability, (I)is present at preferably 5% by mass or greater, more preferably 10% bymass or greater, even more preferably 15% by mass or greater and mostpreferably 20% by mass or greater, with respect to the total of (I) and(II).

[0076] For the R² groups in formulas (A), (B) and (E) there are noparticular restrictions on the (molar) ratio of R² derived from analcohol of component (c-I) and R² derived from an alcohol of component(c-II), but the range of 1:99 to 99:1 is preferred to simultaneouslyachieve satisfactory lubricity, heat and hydrolytic stability andrefrigerant miscibility. From a standpoint focused on miscibility, thisratio is preferably in the range of 60:40 to 99:1, more preferably inthe range of 70:30 to 99:1 and most preferably in the range of 80:20 to99:1. From a standpoint focused on the heat and hydrolytic stability andlubricity, the ratio is preferably in the range of 1:99 to 60:40, morepreferably in the range of 1:99 to 50:50 and most preferably in therange of 1:99 to 40:60.

[0077] According to the invention, when a compound obtained by theaforementioned esterification reaction is represented by any of formulas(A) to (E) above, one type of compound represented by formulas (A) to(D) may be used, or a mixture of two or more types of compoundsrepresented by formulas (A) to (E) may be used. It is not highlypreferred for the alicyclic polycarboxylic acid ester compound of theinvention to contain none of the compounds represented by formulas (A)to (D), being composed only of compounds represented by formula E),because this results in a poor balance between viscosity rise aridrefrigerant miscibility.

[0078] When the alicyclic polycarboxylic acid ester compound of theinvention is a mixture of two or more different compounds represented byformulas (A) to (E), the proportion of each compound may be as desiredand is not particularly restricted, but the contents based on the totalmixture are preferably as follows, from the standpoint of balancebetween refrigerant miscibility and performance, as well as ease ofproduction.

[0079] (A): 0-100 mol %, preferably 1-99 mol % and more preferably 5-95mol %.

[0080] (B): 0-100 mol %, preferably 1-90 mol % and more preferably 2-80mol %.

[0081] (C) 0-100 mol %, preferably 1-99 mol % and more preferably 5-95mol %.

[0082] (D): 0-100 mol %, preferably 1-90 mol % and more preferably 2-80mol %.

[0083] (E): 0-90 mol %, preferably 1-80 mol % and more preferably 5-75mol %,

[0084] The foregoing explanation concerns esterification reaction usingcompound (a) as the acid component and compounds (b) and (c) as alcoholcomponents, but an alicyclic polycarboxylic acid ester compoundaccording to the invention is not limited to being produced by theaforementioned esterification reaction so long as the acid componentstructure in the molecule is derived front compound (a) and the alcoholcomponent structure is derived from compound (b) and/or compound (c),For example, it is possible to obtain an aromatic polycarboxylic acidester compound by esterification reaction between an aromaticpolycarboxylic acid with two carboxyl groups on mutually adjacent carbonatoms of the aromatic ring, and alcohols of compound (b) and (c), andthen to obtain the target alicyclic polycarboxylic acid ester compoundby hydrogen addition (hydrogenation) of the obtained aromaticpolycarboxylic acid ester.

[0085] In the alicyclic polycarboxylic acid ester compound obtained inthis manner, hydrocarbon groups may of course be bonded to one or moreof the carbon atoms of the alicyclic ring. Such hydrocarbon groups arepreferably alkyl groups, with methyl group being particularly preferredin terms of miscibility.

[0086] While there are no particular restrictions on the content of thealicyclic polycarboxylic acid ester compound in a refrigerating machineoil composition according to the invention, it is preferably 5% by massor greater, more preferably 10% by mass or greater, even more preferably30% by mass or greater and most preferably 50% by mass or greater, basedon the total amount of the refrigerating machine oil, as this will helpto bring out the excellent performance of the alicyclic polycarboxylicacid ester compound.

[0087] The alicyclic polycarboxylic acid ester compound in therefrigerating machine oil composition of the invention is used primarilyas a base oil. While the alicyclic polycarboxylic acid ester compoundmay be used alone as the base oil for the refrigerating machine oilcomposition of the invention, it may also be used in combination withoxygen-containing synthetic oils including esters other than thealicyclic polycarboxylic acid ester compound specified by the invention,such as polyol esters and complex esters, polyglycols, polyvinyl ethers,ketones, polyphenyl ethers, silicones, polysiloxanes aridperfluoroethers.

[0088] There are no particular restrictions on the amount ofoxygen-containing synthetic oils included. From the standpoint ofachieving improvement in thermal efficiency as well as heat andhydrolytic stability of the refrigerating machine oil, however, otheroxygen-containing synthetic oils are preferably present at no greaterthan 150 parts by weight, and more preferably no greater than 100 partsby weight, to 100 parts by weight of the alicyclic polycarboxylic acidester compound.

[0089] The refrigerating machine oil composition of the inventioncomprises an alicyclic polycarboxylic acid ester compound and ifnecessary oxygen-containing synthetic oils, and these are used primarilyfor the base oil. The refrigerating machine oil composition of theinvention may also be suitably used with no further additives, or ifnecessary, it may be used in a form combined with various additives. Forfurther enhancement of the abrasion resistance and load resistance ofthe refrigerating machine oil composition of the invention, itpreferably further includes at least one type of phosphorus compoundselected from the group consisting of phosphoric acid esters, acidicphosphoric acid esters, amine salts of acidic phosphoric acid ester,chlorinated phosphoric acid esters and phosphorous acid esters. Thesephosphorus compounds are esters of phosphoric acid or phosphorous acidwith alkanols and polyether alkanols, or derivatives thereof.

[0090] As specific examples of phosphoric acid esters there may bementioned tributyl phosphate, tripentyl phosphate, trihexyl phosphate,triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecylphosphate, triundecyl phosphate, tridodecyl phosphate, tritridecylphosphate, tritetradecyl phosphate, tripentadecyl phosphate,trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate,trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenylphosphate, cresyldiphenyl phosphate and xylenyldiphenyl phosphate. Asacidic phosphoric acid esters there may be mentioned monobutyl acidphosphate, monopentyl acid phosphate, monohexyl acid phosphate,monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acidphosphate, monodecyl acid phosphate, monoundecyl acid phosphate,monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecylacid phosphate, monopentadecyl acid phosphate, monohexadecyl acidphosphate, monoheptadecyl acid phosphate, monooctadecyl acid phosphate,monooleyl acid phosphate, dibutyl acid phosphate, dipentyl acidphosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acidphosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecylacid phosphate, didodecyl acid phosphate, ditridecyl acid phosphate,ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecylacid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphateand dioleyl acid phosphate. As amine salts of acidic phosphoric acidester there may be mentioned amine salts of the above acidic phosphoricesters and amines such as methylamine, ethylamine, propylamine,butylamine, pentylamine, hexylamine, heptylamine, octylamine,dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, trimethylamine,triethylamine, tripropylamine, tributylamine, tripentylamine,trihexylamine, triheptylamine and trioctylamine. As chlorinatedphosphoric acid esters there may be mentioned tris dichloropropylphosphate, tris chloroethyl phosphate, tris chlorophenyl phosphate andpolyoxyalkylene bis[di(chloroalkyl)] phosphate. As phosphorous acidesters there may be mentioned dibutyl phosphite, dipentyl phosphite,dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonylphosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite,dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributylphosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite,trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecylphosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphiteand tricresyl phosphite. Mixtures of these may also be used.

[0091] When such phosphorus compounds are added to the refrigeratingmachine oil composition of the invention there are no particularrestrictions on their content, but such phosphorus compounds willusually be added to a content of 0.01-5.0% by mass and preferably0.02-3.0% by mass, based on the total of the refrigerating machine oilcomposition (based on the total of the base oil and all additives)

[0092] For enhanced heat and hydrolytic stability of the refrigeratingmachine oil composition of the invention, there may also be included oneor more epoxy compounds selected from the group consisting of thefollowing (i) to (viii );

[0093] (i) phenylglycidyl ether-type epoxy compounds

[0094] (ii) alkylglycidyl ether-type epoxy compounds

[0095] (iii) glycidyl ester-type epoxy compounds

[0096] (iv) allyloxirane compounds

[0097] (v) alkyloxirane compounds

[0098] (vi) alicyclic epoxy compounds

[0099] (vii) epoxidized fatty acid monoesters

[0100] (viii) epoxidized vegetable oils

[0101] Specific examples of (i) phenylglycidyl ether-type epoxycompounds include phenylglycidyl ethers and alkylphenylglycidyl ethers.Here, the alkylphenylglycicyl ethers may have 1-3 alkyl groups of 1-13carbons, among which preferred examples include those with one alkylgroup of 4-10 carbons, such as n-butylphenylglycidyl ether,i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether,tertbutylphenylglycidyl ether, pentylphenylglycidyl ether,hexylphenylglycidyl ether, heptylphenylglycidyl ether,octylphenylglycidyl ether, nonylphenylglycidyl ether anddecylphenylglycidyl ether.

[0102] Specific examples of (ii) alkylglycidyl ether-type epoxycompounds include decylglycidyl ether, undecylglycidyl ether,dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether,2-ethylhexylglycidyl ether, neopentylglycoldiglycidyl ether,trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidylether, 1,6-hexanediol diglycidyl ether, sorbitolpolyglycidyl ether,polyalkyleneglycol monoglycidyl ether and polyalkyleneglycol diglycidylether.

[0103] Specific examples of (iii) glycidyl ester-type epoxy compoundsinclude compounds represented by the following general formula (1):

[0104] where R represents a hydrocarbon group of 1-18 carbons.

[0105] In formula (1) above, R represents a hydrocarbon group of 1-18carbons, and as such hydrocarbon groups there may be mentioned alkylgroups of 1-18 carbons, alkenyl groups of 2-18 carbons, cycloalkylgroups of 5-7 carbons, alkylcycloalkyl groups of 6-18 carbons, arylgroups of 6-10 carbons, alkylaryl groups of 7-18 carbons and arylalkylgroups of 7-18 carbons. Preferred among these are alkyl groups of 5-15carbons, alkenyl groups of 2-15 carbons, phenyl groups and alkylphenylgroups with alkyl groups of 1-4 carbons.

[0106] Specific preferred examples among these glycidyl ester epoxycompounds include glycidyl-2,2-dimethyl octanoate, glycidyl benzoate,glycidyl-tert-butyl benzoate, glycidyl acrylate, glycidyl methacrylateand the like.

[0107] Specific examples of (iv) allyloxirane compounds include1,2-epoxystyrene and alkyl-1,2-epoxystyrene.

[0108] Specific examples of (v) alkyloxirane compounds include1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane,1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxydecane,1,2-epoxydodecane, 1,2-epoxytridecane, 1,2-epoxytetradecane,1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane,1,1,2-epoxyoctadecane, 2-epoxynonadecane and 1,2-epoxyeicosane.

[0109] As (vi) alicyclic epoxy compounds there may be mentionedcompounds wherein carbon atoms composing the epoxy group are directlypart of the alicycle, such as compounds represented by the followinggeneral formula (2):

[0110] Specific examples of such alicyclic epoxy compounds include1,2-epoxycyclohexane, 1,2-epoxycyclopentane,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,bis(3,4-epoxycyclohexylmethyl) adipate, exo-2,3-epoxynorbornane, bis (3,4epoxy-6-methylcyclohexylmethyl) adipate,2-(7-oxabicyclo[4.1.0]hept-3-yl)-spiro(1,3-dioxane-5,3′-[7]oxabicyclo[4.1.0]heptane,4-(1′-methylepoxyethyl)-1,2-epoxy-2-methylcyclohexane,4-epoxyethyl-1,2-epoxycyclohexane.

[0111] Specific examples of (vii) epoxidized fatty acid monoestersinclude esters of epoxidized fatty acids of 12-20 carbons and alcoholsof 1-8 carbons, phenols or alkylphenols. Particularly preferred for useare butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl, phenyl andbutylphenyl esters of epoxystearic acid.

[0112] Specific examples of (viii) epoxidized vegetable oils includeepoxy compounds of vegetable oils such as soybean oil, linseed oil andcottonseed oil.

[0113] Among the aforementioned epoxy compounds, phenylglycidyl etherepoxy compounds, glycidyl ester epoxy compounds, alicyclic epoxycompounds and epoxidized fatty acid monoesters are preferred for furtherimproved heat and hydrolytic stability, with glycidyl ester epoxycompounds and alicyclic epoxy compounds being even more preferred.

[0114] When these epoxy compounds are incorporated in a refrigerant oilcomposition according to the invention, there are no particularrestrictions on their addition content but the epoxy compound is addedto a content of preferably 0.1-5.0% by mass and more preferably 0.2-2.0%by mass, based on the total amount of the refrigerating machine oilcomposition (the total amount of the base oil and all incorporatedadditives).

[0115] Two or more different types of the aforementioned phosphoruscompounds and epoxy compounds may, of course, be used in combination.

[0116] In order to further improve performance, the refrigeratingmachine oil composition of the invention may be incorporated, asrequired, with hitherto publicly known additives for refrigeratingmachine oils, for example, phenol-type antioxidants such asdi-tert-butyl-p-cresol and bisphenol A; amine-type antioxidants such asphenyl-a-naphthylamide and N,N-di(2-naphthyl)-p-phenylenediamine; wearresistance agents such as zinc dithiophosphate; extreme pressure agentssuch as chlorinated paraffin and sulfur compounds; oiliness improverssuch as fatty acids; antifoaming agents such as silicone types; metalinactivators such as benzotriazole; viscosity index improvers;pour-point depressants; detergent dispersants and the like, either aloneor in combinations of more than one type. The total amount of theadditives added into the refrigerating machine oil is not particularlylimited, but in general the content is preferably not more than 10% bymass and more preferably not more than 5% by mass, of the total amountof the refrigerating machine oil composition (i.e., the total amount ofthe base oil and all incorporated additives).

[0117] There are no particular restrictions on the kinematic viscosityof the refrigerating machine oil composition of the invention, and thekinematic viscosity at 40° C. may be within a range of 3 to 500mm^(2/)s, more preferably 4 to 400 mm^(2/)s and most preferably 5 to 300mm²/s. Further, the kinematic viscosity at 100° C. may be within a rangeof 1 to 50 mmm^(2/)s, more preferably 1.5 to 40 mm^(2/)s, and mostpreferably 2 to 30 mm^(2/)s.

[0118] Also, the volume resistivity of the refrigerating machine oilcomposition of the invention is not particularly limited, but ispreferably at least 1.0×10¹¹ Ω·cm, more preferably at least 1.0×10¹²Ω·cm and most preferably at least 1.0×10¹³ Ω·cm. Particularly, when therefrigerating machine oil composition is used for a hermetic typerefrigerating machine, a high electric insulating property tends to berequisite. According to the present invention, the volume resistivity isrepresented by the value [Ω·cm] at 25° C. measured in accordance withJIS C 2101 “Electric Insulating Oil Testing Method.”

[0119] The moisture content of the refrigerating machine oil compositionof the invention is not particularly limited, but is preferably nogreater than 200 ppm, more preferably no greater than 100 ppm, and mostpreferably no greater than 50 ppm, of the total amount of therefrigerating machine oil composition. A low moisture content isparticularly required when the refrigerating machine oil composition isused for a hermetic type refrigerating machine, because of its effectson the heat and hydrolytic stability and the electric insulatingproperty of the oil.

[0120] The total acid value of the refrigerating machine oil compositionof the invention is also not particularly limited, but when the oilcomposition is used in a refrigerating machine or in pipes to preventmetals from corrosion, the total acid value is preferably no greaterthan 0.1 mgKOH/g, and more preferably no greater than 0.05 mgKOH/g.According to the invention, the total acid value is represented as thetotal acid value measured in accordance with JIS K 2501 “PetroleumProducts and Lubricating Oils—Neutralization Value Testing Method”.

[0121] The ash content of the refrigerating machine oil composition ofthe invention is not particularly limited, but in order to improve theheat and hydrolytic stability of the oil and reduce generation of sludgeand the like, it is preferably no greater than 100 ppm, and morepreferably no greater than 50 ppm. According to the invention, the ashcontent is represented by the ash content value [ppm] as measured inaccordance with JIS K 2272 “Testing Method for Ash Content and SulfuricAcid Ash Content in Crude Oils and Petroleum Products”.

[0122] Refrigerants that may be used in refrigerating machines thatemploy refrigerating machine oil compositions according to the inventioninclude HFC refrigerants, fluorine-containing ether refrigerants such asperfluoroethers; fluorine-free ether refrigerants such as dimethylethers; and natural refrigerants such as carbon dioxide, hydrocarbonsand the like, and these refrigerants can be used alone or incombinations including two or more kinds of the refrigerants.

[0123] As HF refrigerants there may be mentioned hydrofluorocarbonshaving 1-3 and preferably 1 or 2 carbon atoms. Specific examples includeHFCs such as difluoromethane (HFC-32), trifluoromethane (HFC-23),pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluloroethane (HFC-143a),1,1-difluoroethane (HFC-152a), and mixtures of two or more kinds ofthese HFCs. The refrigerant is selected in accordance with the intendeduse and the required performance, and as preferred examples there may bementioned HFC-32 alone; HFC-23 alone; HFC-134a alone; HFC-125 alone; amixture of HFC-134a/HFC-32=60-80% by mass/40-20% by mass; a mixture ofHFC-32/HFC-125−70% by mass/60-30% by mass; a mixture ofHFC-125/HFC-143a=40-60% by mass/60-40% by mass; a mixture ofHFC-134a/HFC-32/HFC-125=60% by mass/30% by mass/10% by mass; a mixtureof HFC-134a/HFC-32/HFC-125=40-70% by mass/15-35% by mass/5-40% by mass;and a mixture of HFC-125/HFC-134a/HFC-143a=35-55% by mass/1-15% bymass/40-60% by mass. More specific examples include a mixture ofHFC-134a/HFC-32=70/30% by mass; a mixture of HFC-32/HFC-125=60/40% bymass; a mixture of HFC-32/HFC-125=50/50% by mass (R410A); a mixture ofHFC-32/HFC-125=45/55% by mass (R410B); a mixture ofHFC-125/HFC-143a=50/50% by mass (R507C); a mixture ofHFC-32/HFC-125/HFC-134a=30/10/60% by mass; a mixture ofHFC-32/HFC-125/HFC-134a=23/25/52% by mass (R407C); a mixture ofHFC-32/HFC-125/HFC(-134a=25/15/60%, by mass (R407E); and a mixture ofHFC-125/HFC-134a/HFC-143a=44/4/52% by mass (R404A).

[0124] Examples of natural refrigerants include carbon dioxide,hydrocarbons and the like. A hydrocarbon refrigerant referred to here ispreferably a gas at 25° C. under 1 atm. Specifically such gases includealkanes, cycloalkanes and alkenes of 1 to 5 carbons and preferably 1 to4 carbons, as well as mixtures thereof. Specific examples of suchhydrocarbon refrigerants include methane, ethylene, ethane, propylene,propane, cyclopropane, butane, isobutane (i-butane), cyclobutane,methylcyclopropane and mixtures of two or more of these compounds.Propane, butane, isobutane and mixtures thereof are preferred amongthese.

[0125] The refrigerating machine oil composition of the inventionnormally exists in the form of a refrigerating machine fluid compositionmixed with a refrigerant as describe above when it is used in therefrigerating machine. The mixing ratio of the refrigerating machine oilcomposition to the refrigerant is not particularly limited, but theamount of the refrigerating machine oil composition is preferably withina range of 1 to 500 parts by weight and more preferably within a rangeof 2 to 400 parts by weight to 100 parts by weight of the refrigerant.

[0126] The refrigerating machine oil composition of the invention can beused as a lubricating oil for refrigerant compressors in all types ofrefrigerating machines, because of its excellent electric properties andlow hygroscopicity. The refrigerating machines in which the compositionmay be used include, specifically, an air conditioner for rooms, anpackage air conditioners, a cold-storage chest (refrigerator), anautomotive air conditioner, a dehumidifier, a freezer, a freeze andrefrigeration warehouse, an automatic vending machine, a showcase, acooling apparatuses in chemical plants, etc. The refrigerating machineoil composition of the invention is most preferably used inrefrigerating machines equipped with hermetic compressors. Therefrigerating machine oil composition of the invention may be used withall types of compressors including reciprocating types,rotary types andcentrifugal types.

[0127] The construction of the preferred refrigerating cycle in whichthe composition of the invention is used will typically be equipped witha compressor, a condenser, an expander and an evaporator, and ifnecessary a drier.

[0128] The compressor may be, for example, a high-pressurecontainer-system compressor wherein a motor comprising a rotator and astator, a rotating shaft fitted in the rotator, and a compressor sectionconnected to the motor are housed in a sealed container holding arefrigerating machine oil, and high-pressure refrigerant gas ejectedfrom the compressor section is collected in the sealed container, or alow-pressure container-system compressor wherein a motor comprising arotator and a stator, a rotating shaft fitted in the rotator, and acompressor section connected to the motor are housed in a sealedcontainer holding a refrigerating machine oil, and high-pressurerefrigerant gas ejected from the compressor section is directly ejectedout of the sealed container.

[0129] An insulating film used as the electric insulating systemmaterial for the motor section may be a crystalline plastic film with aglass transition point of 50° C. or higher, specific preferred examplesof which include one or more types of insulating films selected from thegroup consisting of polyethylene terephthalate, polybutyleneterephthalate, polyphenylene sulfide, polyether-ether-ketone,polyethylene naphthalate, polyamideimide and polyimide, or compositefilms prepared by laminating high glass transition point resin layers onlow glass transition point films, because of their resistance todeterioration in tensile strength and electric insulating property. Themagnet wire which is used for the motor section is preferably one withan enamel coating having a glass transition point of 120° C. or higher,such as a monolayer of a polyester, polyester imide, polyamide orpolyamideimide, or an enamel coating which is a composite coating of ahigh glass transition point upper layer on a low glass transition pointunderlayer. As composite coated enamel wires there may be mentionedthose with a polyamideimide upper layer coated on a polyester imideunderlayer (AI/EI), and those with a polyamideimide upper layer coatedon a polyester underlayer (AI/PE.) The drying agent packed in the drieris preferably synthetic zeolite comprising an alkali metalsilicate/aluminate compound salt with a carbon dioxide gas absorptionvolume of no greater than 1.0% at a pore size of 3.3 Angstroms orsmaller and a carbon dioxide gas partial pressure of 250 mmHg at 25° C.Specific examples include the trade names XH-9, XH-10, XH-11 and XH-600by Union Showa Co., Ltd.

EXAMPLES

[0130] The present invention will now be explained in further detail byway of examples and comparative examples, with the understanding thatthe invention is in no way limited thereby.

Examples 1-14 and Comparative Examples 1-2

[0131] Sample oils were prepared for Examples 1-14 and ComparativeExamples 1-2, using each of the following base oils and additivescombined in the mixing ratios shown in Tables 1 to 4. The properties ofeach of the obtained sample oils (kinematic viscosity at 40° C. and 100°C., total acid value) are shown in Tables 1-4.

[0132] (Alicyclic Polycarboxylic Acid Ester Compounds)

[0133] The alicyclic polycarboxylic acid ester compounds for Examples1-14 were obtained using the compounds listed below as compounds (a),(b) arid (c) (components (c-I) and (c-II)), in the mixing ratios listedin Tables 1 to 3. All of the alicyclic polycarboxylic acid esters usedcontained compounds represented by formulas (A) to (E). Tables 1 to 3show the compositions of compounds (A) to (E) for each of the examples.In Tables 1 to 3, E (c-I, c-I) represents a compound wherein both of thetwo R² groups of compound (E) are alkyl groups derived from component(c-I), E (c-I, c-II) represents a compound wherein one of the two R²groups of compound (E) is an alkyl group derived from component (c-I)and the other is an alkyl group derived from component (c-II), and E(c-II, c-II) represents a compound wherein both of the two R² groups ofcompound (E) are alkyl groups derived from component (c-II).

[0134] Compound (a)

[0135] 1: 4-cyclohexene-1,2-dicarboxylic acid

[0136] 2: 1,2-cyclohexanedicarboxylic acid

[0137] Compound (b)

[0138] b-1: ethylene glycol

[0139] b-2: propylene glycol

[0140] b-3: dipropylene glycol

[0141] b-4: butylene glycol

[0142] Compound (c-I)

[0143] c-I-1: iso-butylalcohol

[0144] Compound (c-II)

[0145] c-II-1:2-ethylhexanol

[0146] c-II-2; 3,5,5-trimethylhexanol

[0147] (Other base oils)

[0148] Base oil 1: Ester obtained using mixture of pentaerythritol andmixed acid of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid(mixing ratio: 50/50 (by weight))

[0149] Base oil 2: Copolymer of vinyl ethyl ether and vinyl butyl ether(average molecular weight: 900, ethyl/butyl molar ratio: 7/1)

[0150] Base oil 3: Ester obtained using 4-cyclohexene-1,2-dicarboxylicacid and 2-ethylhexanoic

[0151] Base oil 4: Ester obtained using 4-cyclohexene-1,2-dicarboxylicacid and iso-butanol

[0152] (Additives)

[0153] Additive 1: Glycidyl-2,2-dimethyloctanoate

[0154] Additive 2: Cyclohexene oxide

[0155] Additive 3: Tricresyl phosphate

[0156] The following tests were then carried out for each of the sampleoils of Examples 1-14 and Comparative Examples 1-2.

[0157] (Refrigerant Miscibility Test)

[0158] The refrigerant miscibility of each of the sample oils wasevaluated in accordance with the “Refrigerant Miscibility TestingMethod” of JIS-K-2211 “Refrigerating machine oils”, using HFC-134a orR410A (HFC-32/HFC-125=50/50% by mass mixture) as the refrigerant.Specifically, 10 g of each of the sample oils was blended with 40 g ofthe refrigerant and upon gradually lowering the temperature from 20° C.to −70° C., the temperature at which separation or turbidity occurredwas recorded. The results are shown in Tables 1 to 4. In Tables 1 to 4,“<−70” indicates that no separation or turbidity was exhibited even whenthe temperature was lowered to −70° C., while “>20” indicates thatseparation or turbidity was already exhibited at the initial measuringtemperature (20° C.).

[0159] (Insulating Property Test)

[0160] The volume resistivity of each of the sample oils at 25° C. wasmeasured in accordance with JIS-C-2101 “Electric Insulating Oil TestingMethod.” The results are shown in Tables 1 to 4.

[0161] (Heat/Hydrolytic Stability Test)

[0162] A 90 g portion of each of the sample oils prepared with amoisture content of 500 ppm was weighed out into an autoclave which wassealed after addition of 10 g of HFC134a refrigerant and catalysts(iron, copper and aluminum wires), and then the autoclave was heated at175° C. for 3 weeks and the total acid value of each sample oil wasmeasured. The results are shown in Tables 1 to 4.

[0163] (Lubricity Test)

[0164] A test machine was operated at a test oil temperature of 100° C.under a load of 150 lb for 1 minute and then under a load of 250 lb for2 hours, in accordance with ASTM D 2670, “FALEX WEAR TEST”. The degreeof wear of the test journal (pin) after the test was measured for eachsample oil. The results are shown in Tables 1 to 4. TABLE 1 Example 1Example 2 Example 3 Example 4 Example 5 Composition Alicyclicpolycarboxylic acid 100 100 100 100 100 ester compound (mol %) Charged(a) a-1 100 100 100 100 100 composition a-2 — — — — — (molar (b) b-1 1520 — — — ratio) b-2 — — 15 — — b-3 — — — 15 15 b-4 — — — — — (c-I) c-I-170 60 35 35 35 (c- c-II-1 — — 35 35 — II) c-II-2 — — — — 35 Composition(A) 14 18 8 15 10 of (B) 3 9 20 8 7 (A)-(E) (C) 30 30 28 22 25 (mol %)(D) 6 9 — 3 1 (E) E (c-I, c-I) 47 34 6 10 16 E (c-I, c-II) — — 27 23 26E (c-II, c- — — 11 19 15 II) Other base oils Base oil 1 — — — — — (mol%) Base oil 2 — — — — — Base oil 3 — — — — — Base oil 4 — — — — —Additives (mol %) Additive 1 — — — — — Additive 2 — — — — — Additive 3 —— — — — Kinematic viscosity (mm²/s)  40° C. 38.6 70.9 56.3 44.1 62.3100° C. 4.7 6.4 6.4 5.6 6.9 Total acid value (mgKOH/g) 0.00 0.00 0.000.00 0.00 Turbidity or separation HFC-134a <−70 <−70 −42 −30 −41temperature in miscibility R410A <−70 <−70 −23 2 −31 test (° C.) Volumeresistivity (Ω · cm) 2.7 × 10¹³ 3.1 × 10¹³ 1.2 × 10¹³ 3.3 × 10¹³ 4.6 ×10¹³ Total acid value after heat/hydrolytic 0.94 0.85 0.79 0.32 0.38stability test (mgKOH/g) Wear in lubricity test (mg) 24 22 25 19 18

[0165] TABLE 2 Example 6 Example 7 Example 8 Example 9 Example 10Composition Alicyclic polycarboxylic acid 100 100 100 100 99.5 estercompound (mol %) Charged (a) a-1 — — — 100 100 composition a-2 100 100100 — — (molar (b) b-1 — — — — 20 ratio) b-2 — — — — — b-3 10 15 10 — —b-4 — — — 15 — (c-I) c-I-1 52 35 40 35 60 (c- c-II-1 28 — — 35 — II)c-II-2 — 35 40 — — Composition (A) 8 12 8 13 18 of (B) 5 7 4 6 9 (A)-(E)(C) 17 21 18 20 30 (mol %) (D) — 2 — — 9 (E) E (c-I, c-I) 36 11 27 13 34E (c-I, c-II) 24 26 28 15 — E (c-II, c- 10 21 15 23 — II) Other baseoils Base oil 1 — — — — — (mol %) Base oil 2 — — — — — Base oil 3 — — —— — Base oil 4 — — — — — Additives (mol %) Additive 1 — — — — 0.5Additive 2 — — — — — Additive 3 — — — — — Kinematic viscosity (mm²/s) 40° C. 26.3 60.4 36.0 45.9 70.1 100° C. 4.1 6.8 5.1 5.6 6.3 Total acidvalue (mgKOH/g) 0.00 0.00 0.00 0.00 0.00 Turbidity or separationHFC-134a −64 −51 −51 −19 <−70 temperature in miscibility R410A −40 −32−28 5 <−70 test (° C.) Volume resistivity (Ω · cm) 2.8 × 10¹³ 4.4 × 10¹³4.5 × 10¹³ 1.3 × 10¹³ 3.0 × 10¹³ Total acid value after heat/hydrolytic0.29 0.34 0.59 0.63 0.00 stability test (mgKOH/g) Wear in lubricity test(mg) 26 24 25 22 22

[0166] TABLE 3 Example 11 Example 12 Example 13 Example 14 CompositionAlicyclic polycarboxylic acid 99.5 98.5 50 50 ester compound (mol %)Charged (a) a-1 100 100 100 100 composition a-2 — — — — (molar (b) b-1 —— — — ratio) b-2 — — 15 — b-3 15 15 — 15 b-4 — — — — (c-I) c-I-1 35 3535 35 (c- c-II-1 35 35 35 — II) c-II-2 — — 35 — Composition (A) 15 15 810 of (B) 8 8 20 7 (A)-(E) (C) 22 22 28 25 (mol %) (D) 3 3 — 1 (E) E(c-I, c-I) 10 10 6 16 E (c-I, c-II) 23 23 27 26 E (c-II, c- 19 19 11 15II) Other base oils Base oil 1 — — 50 — (mol %) Base oil 2 — — — 50 Baseoil 3 — — — — Base oil 4 — — — — Additives (mol %) Additive 1 — 0.5 — —Additive 2 0.5 — — — Additive 3 — 1.0 — — Kinematic viscosity (mm²/s) 40° C. 43.3 43.0 62.2 65.6 100° C. 5.5 5.5 7.3 7.6 Total acid value(mgKOH/g) 0.00 0.00 0.00 0.00 Turbidity or separation HFC-134a −30 −30−29 −41 temperature in miscibility R410A 2 2 −10 −33 test (° C.) Volumeresistivity (Ω · cm) 2.9 × 10¹³ 3.1 × 10¹³ 9.3 × 10¹³ 3.5 × 10¹³ Totalacid value after heat/hydrolytic 0.00 0.00 0.48 0.29 stability test(mgKOH/g) Wear in lubricity test (mg) 19 8 22 28

[0167] TABLE 4 Comp. Comp. Ex.1 Ex.2 Composition Alicyclicpolycarboxylic acid 0 0 ester compound (mol %) Charged (a) a-1 — —composition a-2 — — (molar (b) b-1 — — ratio) b-2 — — b-3 — — b-4 — —(c-I) c-I-1 — — (c- c-II-1 — — II) c-II-2 — — Composition (A) — — of (B)— — (A)-(E) (C) — — (mol %) (D) — — (E) E (c-I, c-I) — — E (c-I, c-II) —— E (c-II, c- — — II) Other base oils Base oil 1 — — (mol %) Base oil 2— — Base oil 3 100 — Base oil 4 — 100 Additives (mol %) Additive 1 — —Additive 2 — — Additive 3 — — Kinematic viscosity (mm²/s)  40° C. 16.59.1 100° C. 3.3 2.1 Total acid value (mgKOH/g) 0.00 0.00 Turbidity orseparation HFC-134a >20 <−70 temperature in miscibility R410A >20 <−70test (° C.) Volume resistivity (Ω · cm) 3.5 × 10¹³ 3.4 × 10¹¹ Total acidvalue after heat/hydrolytic 0.29 1.52 stability test (mgKOH/g) Wear inlubricity test (mg) 28 30

[0168] As clearly shown by the results in Tables 1 to 3, the sample oilsof Examples 1 to 14 representing refrigerating machine oil compositionaccording to the invention were confirmed to have a satisfactory balancebetween refrigerant miscibility, electric insulating property,hydrolytic stability, heat stability and lubricity when used togetherwith the HFC refrigerants, even when the viscosity was high.Furthermore, the sample oils of Examples 10 to 12 employing epoxycompounds as additives exhibited even higher heat and hydrolyticstability, while the sample oil of Example 12 employing a phosphoruscompound exhibited even higher lubricity.

[0169] In contrast, as shown in Table 4, the sample oil of ComparativeExample 1 exhibited insufficient refrigerant miscibility, despite itslower viscosity compared to the sample oils of Examples 1 to 14. Thesample oil of Comparative Example 2 exhibited insufficient heat andhydrolytic stability.

[0170] Industrial Applicability

[0171] As explained above, refrigerating machine oil compositionaccording to the present invention can be used together with HFCrefrigerants and natural refrigerants such as carbon dioxide andhydrocarbons, to provide a satisfactory balance between all of theproperties of lubricity, miscibility with refrigerants, heat andhydrolytic stability and electric insulating property.

1. A refrigerating machine oil composition comprising an alicyclicpolycarboxylic acid ester compound obtained from the following compounds(a) to (c): (a) an alicyclic polycarboxylic acid having an alicyclicring and two or more carboxyl groups, or its derivative, wherein atleast two of the carboxyl groups are bonded to mutually adjacent carbonatoms on the alicyclic ring; (b) a compound with two or more hydroxylgroups or its derivative; and (c) a compound with one hydroxyl group orits derivative.
 2. A refrigerating machine oil composition according toclaim 1, wherein the number of carboxyl groups of compound (a) is 2, andthe number of hydroxyl groups of compound (b) is
 2. 3. A refrigeratingmachine oil composition according to claim 1, wherein compound (c) is amixture of at least one type of monohydric alcohol selected from thegroup consisting of aliphatic monohydric alcohols of 1-5 carbons and atleast one type of monohydric alcohol selected from the group consistingof aliphatic monohydric alcohols of 6-18 carbons.
 4. A refrigeratingmachine oil composition according to claim 1, which further comprises atleast one selected from the group consisting of phosphoric acid esters,acidic phosphoric acid esters, amine salts of acidic phosphoric acidester, chlorinated phosphoric acid esters and phosphorous acid esters.5. A refrigerating machine oil composition according to claim 1, whichfurther comprises at least one selected from the group consisting ofphenylglycidyl ether-type epoxy compounds, alkylglycidyl ether-typeepoxy compounds, glycidyl ester-type epoxy compounds, allyloxiranecompounds, alkyloxirane compounds, alicyclic epoxy compounds, epoxidizedfatty acid monoesters and epoxidized vegetable oils.